The present invention relates generally to laminating resins, such as are used in tub, shower, and marine applications, and more particularly to a laminating resin low in styrene content for low VOC (volatile organic content) formulations.
The amount of styrene necessary to dilute laminating resins, such as unsaturated polyester resins, to an appropriate application viscosity (˜250 cps) is of concern from an environmental and safety viewpoint. Typical laminating resins in this art require between about 35% and 60% styrene. Attempts to address this concern have led to developments that are commercially expensive to implement.
The parts produced from laminating resins generally are referred to as fiber-reinforced composite parts. The reinforcing fiber includes, inter alia, glass, carbon, polymeric and like fibers. Such fiber-reinforced parts can be made from a variety of materials and by several processes. The processes for making fiber-reinforced composites can be divided into two general types: closed-mold and open-mold processes. In a closed-mold process the composite part is fabricated in a manner in which the resin prior to cure is not exposed to the ambient environment. Common closed-mold processes include sheet molding, bulk molding structural reaction injected molding (SRIM), resin transfer molding (RTM), and various vacuum-assisted molding processes. Styrene emissions are of lesser concern in closed molding processes since uncured resin is not exposed to the environment.
Open-mold processes are the second general classification of molding processes. Common open-mold processes include spray-up, hand lay-up, rotational molding, filament winding, and the like. In open-mold processes one side of the laminate remains exposed to the environment. Thus, the styrene in the laminating resin can evaporate. Styrene has been classified as a hazardous air pollutant (HAP). Reducing the styrene content of laminating resins is believed to result in lower HAP emissions and a cleaner environment.
Spray-up is commonly used to fabricate parts using a laminating resin and fiberglass reinforcement. In this process a “chopper-gun” is used. The surface of a mold is sprayed with a mixture of laminating resin and chopped glass fiber. Just prior to application, additives are mixed into the resin to promote hardening (i.e., cure). Once the mold surface is covered with an appropriate amount of glass fiber and resin the surface can be rolled to help entrapped air escape. This step is called “rollout”. Alternatively, mats of woven fiberglass can be used. The laminating resin then is applied to the mat and the surface is rolled to remove entrapped air. In either fashion multiple layers can be built up. These layers can be of the same or different material. Since the mold can have uneven surfaces, it is desirable that the laminating resin possesses the ability to fill the resulting voids. Also, it is important that the resin remain uncured and fluid for sufficient time to permit placing of the second layer into contact with the first layer. A resin that hardens too quickly does not permit flexibility in the fabrication process. Thus, the length of time the resin is fluid is measured and is referred to as “gel-time”. After the laminating resin has gelled it is no longer fluid but not hard. Hardening (cure) takes place after the resin has gelled. Usually the part is sufficiently hard so that it can be removed from the mold within 2 to 24 hours of gelation. Hardening times can be shortened by placing the composite parts in an oven maintained at, e.g., 50°-100° C. for, e.g., 1-3 hours. When large parts are being fabricated the use of an oven may not be practical.